The present invention relates to a stepping mechanism. Such stepping mechanisms serve to rotate a toothed wheel in a stepwise manner; a machine element, for example, a parts magazine or the like, which is to be positioned, is in a drive connection with the shaft of the toothed wheel by way of a gear unit. The publication of "Constructional Elements of Precision Mechanics", Richter and Voss, 1959, page 477, discloses stepping mechanisms comprising two wheels whose axes intersect. The driving wheel carries two parallel ribs at its outer surface area, which are connected by means of an inclined intermediate piece. These ribs engage in corresponding gaps of the driven toothed wheel. During the rotation of the driving wheel, the toothed wheel is only shifted further when the inclined intermediate piece is engaged. The shifting distance corresponds to the distance between two parallel ribs. After shifting, the toothed wheel is locked again. Such stepping mechanisms are used predominantly in motion picture technology for shifting the film strip by one frame in each instance. They require a relatively narrow tooth pitch, which sharply restricts their range of application.
In addition, there are single-tooth gear units, of which the Geneva movement star wheels are the most well-known. In this case, the driving wheel carries a peg, instead of a tooth, while the driven wheel, the so-called star wheel, comprises four slots. In order to secure the catch position the driving wheel is provided with a cylindrical projection which engages in a recess of the star wheel in each catch position. Such gear units require very accurate manufacturing. The wheels consist, as a rule, of precision-cut parts whose surfaces, which contact one another, are subjected to fine machining in order to reduce the friction.
Finally, tooth ratchet mechanisms are known, in which the stepwise shifting of a toothed wheel is effected by means of an oscillating member which engages in the teeth of the toothed wheel with a pawl. Since the toothed wheel is not secured when the member swings back, a special stop pawl must be applied which engages in corresponding tooth gaps of the toothed wheel. Whereas in ratchet mechanisms with a shifting pawl and a stop pawl the oscillating shifting member carries along and accordingly shifts the toothed wheel by means of the shifting pawl during forward movement, but, during reverse movement, runs idle and while the toothed wheel is at rest, the toothed wheel is shifted further in both oscillating directions of the shifting member in ratchet mechanisms with two pawls. A shifting pawl shifts in each instance, while the other runs idle.